Fill it up, please!

Throughout the Cold War, in-flight refuelling was aimed largely at increasing the radius of action of strike aircraft and extending the time-on-station of orbiting combat aircraft. The recent series of out-of-area operations involving Nato forces has switched the emphasis to facilitating long-range deployments, a consideration that now affects a larger number of services.

Although growing numbers of countries are voicing needs for tankers, the global market remains dominated by America. The US Air Force has approximately 543 KC-135E/R Stratotankers and 59 McDonnell Douglas KC-10A Extenders, the latter being about half as old. It may be noted that France has three KC-135Rs, and 14 other countries operate small numbers of B707 tanker conversions, notably Iran with 14 707-3J9Cs, Israel with eight 707-320s and Saudi Arabia with eight KE-3As.

KC-135

The US Air Force has 131 KC-135Es on its books, still equipped with Pratt & Whitney TF33-PW-102 turbofans and now operated by the Air National Guard (115) and Air Force Reserve (16). The KC-135Rs, mostly operated by active US Air Force units (245 aircraft, compared to 115 with the Air National Guard and 52 with Reserve units), are re-engined with more economical and more powerful CFM International CFM56-2 engines, and are capable of transferring over 20 per cent more fuel in a 4000 km radius.

It is anticipated that only a small number of these aircraft will reach their service life limits (36,000 and 39,000 hr for the KC-135E and -135R respectively) before 2040. However, the KC-135 is becoming increasingly expensive to use. In 2001 the total annual operation and support cost per aircraft (including personnel, fuel, maintenance, modifications and spare parts) was put at $ 4.6 million for the KC-135E and $ 3.7 million for the KC-135R. At any one time in 1990 some 90 US Air Force KC-135s were out of service due to heavy maintenance work, and this figure rose to 175 in 2000. It is expected that this number will exceed 200 aircraft in 2005.

Ever since 1990 there seems to have also been a US Air Force belief that a tanker version of the Boeing 767-200ER would provide the best replacement for the KC-135R. The significant factor appears to have been that the two aircraft are similar in size, airfield requirements and fuel off-load capability. One of the recent criticisms of US Air Force planning was that there had been no proper analysis of alternatives, comparing the KC-767A with tanker derivatives of the Boeing C-17 and 7E7, and of pre-used Douglas DC-10s and McDonnell Douglas MD-11s. It may be noted that Boeing regards the stretched 767-300ER as unsuited to tanker conversion, due to its reduced tail clearance at unstick ruling out the installation of a boom.

KC-767

The KC-767A has a maximum take-off weight of 184,600 kg, compared to 146,285 kg for the KC-135R. It will also be able to operate from relatively short airfields, requiring only a 2800-metre runway at maximum take-off weight, compared to 3500 metres for the KC-135R. Unlike most KC-135s, the KC-767A will be able to perform both boom and drogue refuelling on the same sortie, but fuel offload is only marginally improved. Taking off from a 2500 metre runway, the KC-767A will offload 53 tonnes at 925 km radius, compared to 50 tonnes for the KC-135R.

The big difference between the two aircraft is in usable cabin volume; the KC-135 being limited by the presence of fuel tanks to six standard military 463-L pallets, whereas the KC-767A (with all its fuel under the floor) can carry up to 19 pallets. Likewise, the KC-767A can alternatively accommodate up to 200 passengers, compared to only 57 for the KC-135R. Whereas the old KC-135E loses over 400 days in heavy maintenance every five years (up from 158 in 1991), the KC-767A is expected to lose only 70 days every ten years.

In 2001 Congress authorised the US Air Force to explore the leasing of 100 KC-767As. Boeing claimed that--in a worst-case scenario--leasing could cost the service $1.9 billion more than a traditional multi-year buy, but that this did not allow for a $ 5.5 billion saving on maintenance and upgrading of 100 KC-135Es. Leasing would also introduce the KC-767A five years earlier, and by the time that the first conventionally-acquired tanker would have been delivered there would be 60 leased aircraft already in service.

In 2002 a competing Eads proposal to the US Air Force, based on the Airbus A330-200 MRTT, was rejected on the grounds that Eads did not have an operational refuelling boom, and that the aircraft would introduce undesirably large paving loads and parking area demands.

Late in 2003, as Congressional opposition to the KC-767A lease grew, the Boeing proposal was modified, so that only 20 aircraft would be leased in order to obtain early deliveries, the remaining 80 being purchased through the normal channels. However, this new concept was rejected by the Pentagon.

The service's critics argue that the corrosion problem of the KC-135E has been exaggerated and is manageable (at least in the short term). The FY2005 budget will nonetheless include $100 million to make a start on the KC-X programme, which is expected to be launched in FY2006 leading to a multi-year buy rather than leasing. By the end of March 2004, Boeing had invested $ 310 million on the KC-767A programme, but then began redeploying workers. If no US Air Force KC-767A order is forthcoming in the near future, Boeing may be forced to close the 767 production line.

While the US Air Force was looking for ways to obtain tankers without using funds needed for more important (i.e., fighter) programmes, the first KC-767 export sales had gone ahead. Boeing's 767 Tanker Transport programme was launched in 2001 when the 767-200ER Convertible Combi version with General Electric CF6-80C2 turbofans was selected by Italy, which has a requirement for four. The Combi can carry a mixed load of (for example) 97 passengers and ten cargo pallets. The Italian version, for which the contract was signed on 11 December 2002, will have a centreline boom (an improved fly-by-wire version of the KC-135 boom) and two wing-mounted hose-and-drogue pods, plus a third hose-and-drogue unit on the fuselage. The first aircraft taken from the commercial production line is being modified to tanker configuration at Wichita, but the remaining three are to be modified by Aeronavali at Naples. The first flight is due to take place before the end of 2004, the first delivery in early 2005, and the last in 2008.

Japan selected the 767-200ER in December 2001, also with CF6-80C2 engines; doubtless encouraged by the resulting commonality with its four E-767 AEW&C aircraft, deliveries of which had begun in 1998. In this case the Convertible Freighter version was chosen, with a cabin that can be configured for all-freight or all-passengers but not a mix. It also differs from the Italian aircraft in having auxiliary underfloor tanks and only the centreline refuelling boom. The first delivery for Japan is scheduled for 2006.

For any 767 Tanker Transport, Smiths Aerospace is responsible for the hose-and-drogue units and the refuelling system, in which the boom is controlled by an operator on the flight deck. The system is known as Raro II (Remote Aerial Refuelling Operator II), Raro I being the system used on Dutch KDC-10s.

The KC-767A proposed for the US Air Force is somewhat like the Italian aircraft in having the Convertible Combi cabin, but it has the auxiliary underfloor tanks of the Japanese version, giving a total of 91,625 kg of fuel. It has only the fuselage-mounted boom and hose-and-drogue unit, not the underwing pods (although these may be introduced with development Spiral Two). Unlike the early export aircraft, it also has a refuelling receptacle in the upper front fuselage, and the advanced cockpit, strengthened main undercarriage and auxiliary power unit of the 767-400. Uprated 120 kva alternators allow for growth in power demands. It has recently been announced that the KC-767A will also differ from the Italian and Japanese tankers in having Pratt & Whitney PW4062 turbofans, although the eventual US Air Force fleet of around 400 new wide-body tankers may be part P&W- and part GE-engined.

A330-200 MRTT

Europe's principal tanker initiative is the Airbus A330-200 MRTT, which has a maximum take-off weight of 233,000 kg, making it more than 25 per cent heavier than the KC-767A. Its span of 60.30 metres may be compared to the 47.57 of the Boeing project, and their lengths are 59.00 and 48.51 metres respectively. Fuel capacity of the A330 tanker is unchanged at 111,000 kg, all contained in wing tanks. It is claimed that the same fuel offload as that of the KC-767A can be provided with around 20 per cent fewer sorties. The wing of the twin-engined A330 is basically the same as that of the four-engined A340, and the two hose-and-drogue pods of the MRTT will be carried on the attachments for the latter's outboard engines.

Eads is investing about $ 84 million in the development of an advanced refuelling boom system (ARBS), which will feature a 127 mm diameter pipe and a fuel transfer rate of 4550 litres/min. Rig tests are scheduled for November 2004, followed by first flight on an A310-300 by the end of 2005. This boom will be used on the Australian version of the A330-200 MRTT.

On 26 January 2004 it was announced that the Global AirTanker Service consortium bid had been tentatively selected to provide the Royal Air Force with a Future Strategic Tanker Aircraft (FSTA). AirTanker is owned 40 per cent by Eads, 20 per cent by Rolls-Royce, 20 by Cobham (who own Flight Refuelling), 10 by Thales and 10 per cent by the VT Group. The bid is based on A330-200 MRTTs with RollsRoyce Trent 772B turbofans, forming a fleet that will replace 20 BAC VC10s and six Lockheed TriStars.

The FSTA is currently seen as Britain's largest private finance initiative, although the negotiations threaten to be equally record-breaking. The programme is expected to last 27 years and cost around $23 billion, with the RAF paying only for the services it requires, and some aircraft being released for commercial charters when not required by the service. Whatever its final commercial form (and the Ministry of Defence's past record hardly inspires confidence that it will eventuate as planned), it will involve around 16 aircraft, some of which may be pre-used.

Around two-thirds of the fleet will have two hose-and-drogue units under the wings, and can thus quickly be converted for civil use. The remainder will have a third unit under the fuselage, for refuelling large aircraft such as the Airbus A400M and Lockheed Martin C-130J. There is no British requirement for a boom to refuel the Boeing C-17, which will presumably rely on US Air Force tankers. The contractor is expected to employ around a quarter of the pilots and ground crew, who will be military reservists. The FSTA service is expected to begin in late 2009.

In April 2004 Eads was selected to supply five A330-200 MRTTs to satisfy the Australian Defence Force's Air 5402 requirement, a decision based on lower platform cost and superior capability. The alternative was the US Air Force-specified KC-767A, for which Australia would have had to fund development. In addition, the more capable A330 was judged to be able to deploy six Boeing F/A-18C/Ds from Darwin to Butterworth (Malaysia), while carrying 43 tonnes of payload. The RAAF version will differ from the RAF aircraft in having the ARBS to refuel the General Dynamics F-111, Boeing 737-700 AEW&C and the F-35A. Underwing drogue pods on the MRTT will refuel the F/A-18. The RAAF aircraft will also have General Electric CF6-80E1 turbofans, giving commonality with Qantas 767s, although the latter will be withdrawn by the end of the decade. Under a separate contract, Qantas Defence Services will convert all but the first aircraft to tankers and provide 20-year support.

Alternatives

Encouraged by reported problems in British FSTA negotiations, the Dublin-based Omega Air has teamed with the US company Evergreen International to form a joint venture named Global AirTanker Service (Gas), offering converted DC-10s as interim tanker transports. As exhibited at Farnborough 2004, these 260,800 kg KDC-10s would have two Flight Refuelling Mk 32-900 underwing pods and a flying boom with a control system developed by Evergreen. Gas is also offering a pay-by-the-hour tanker service to the US Air Force and US Navy, and hopes to modify up to 15 ex-Japan Air Lines DC-10-40s. Flight trials are scheduled to start in late 2005.

The Airbus A310 MRTT is marginally lighter and less capable than the KC-767A, with a maximum take-off weight of 164,000 kg, a fuel load of 77,660 kg with four auxiliary underfloor tanks, and the ability to offload 45 tonnes at 1850 km radius. It is powered by two General Electric CF6-80C2s. Six A310-304s are currently being converted to MRTTs by Airbus Germany and Lufthansa Technik. Four are for the German Air Force and two for the Canadian Armed Forces. The first flight took place on 20 December 2003, and all six are to be delivered by mid-2005.

The A310 MRTT also appears to be a likely front-runner in a Nato contest for up to ten dedicated tankers that would be the subject of a lease-to-buy deal, in an initiative led by Spain and supported by Denmark, Hungary, Luxembourg, Norway, Poland and Portugal. However, Eads may also offer the A330-200 MRTT. Boeing is expected to submit the Italian version of KC-767 and IAI's converted pre-used 767-200s.

The only other tanker transport in production is the Lockheed Martin

KC-130J Hercules for the US Marine Corps. A much lighter aircraft than those discussed above, the KC-130J has a maximum take-off weight of 79,300 kg. If equipped with two underwing tanks (which are not normally seen on the C-130J series), it can offload through its pair of Mk 32B-901E pods 26,000 kg of fuel at 925 km radius. An auxiliary tank in the cabin would add 11,060 kg of fuel. The US Marine Corps currently has a fleet of 79 KC-130F/R/Ts, which are to be replaced by 52 KC-130Js. Orders currently stand at 33 units, of which 13 have so far been delivered. The KC-130 series has traditionally been limited to refuelling helicopters and fixed-wing aircraft such as the Boeing AV-8B, but the KC-130J is also suitable for the F/A-18, and will refuel the (probe-equipped) F-35B/C.

Returning to the US Air Force KC-X programme, if a decision is deferred for several years, it is possible that a tanker version of the Boeing 7E7 could be available by 2013-14. On an even longer timescale (beyond 2015), Boeing could produce a completely new tanker transport based on the Blended Wing Body (BWB) concept. A small-scale technology demonstrator may fly as early as 2005. Lockheed Martin's new projects include the Joined Wing Concept, which, like the BWB, would have two booms and could be developed if the US Air Force demanded a major advance in tanker transports.

Who, What, Where?

Type                          Main Users                Units/Status

KC-135E/R Stratotanker        US Air Force                       543
KC-10A Extender               US Air Force                        59
KC-135R                       France                               3
707-3J9C conversions          Iraq             14 + 11 other nations
707-320                       Israel                               8
KE-3A                         Saudi Arabia                         8
767-200ER Convertible Combi   Italy                   4--requirement
767-200ER Convertible Combi   Japan                         selected
A330-200 MRTT                 Australia                  5--selected
A330-200 MRTT (FSTA)          Britain                      competing
KDC-10                        Britain                      competing
A310 MRTT                     Germany                      4 ordered
A310 MRTT                     Canada                       2 ordered
KC-1307                       US MarineCorps              33 ordered

Brief Comparison

Type             Max Tow

KC135R          146,285 kg
KC-767A         184,600 kg
A330-200 MRTT   233,000 kg
A310 MRTT       164,000 kg
KDC-10          260,800 kg
KC-130J          79,000 kg